I can identify with all of the above having suffered from HA for many years now.
I've been through all of these stages and I wish I could say I've found the solution.
What I can say is that the sting in the scorpion's tail has become weaker. In other words I don't react with as much panic and to every little symptom the way I used to.
I look on this as a phobia. How do you deal with a phobia? You desensitize. Which isn't a problem when you have one phobia like spiders or rats. But there are so many hundreds of thousands of diseases to suffer from, one can't suffer through each and every one before coming to terms with one's fear.
Still, in the last 18 odd years I've managed to get through a good few of the more common ailments so that I can almost relax when I have colds and flu, IBS, migraines. I still "over-react" and imagine that a cold could be something far more important...... but I can reason with myself now.
I've been through the stage of going to the doctor just for reassurance and now I'm in a stage of denial; where I don't want to go just in case they do find something or even suspect something which will send me into a spiral of panic and anxiety. I won't even have my blood pressure taken in case it's not normal because that will cause more panic.
And the panic over all these years has caused its own set of health issues. I go through stages of dizziness and feeling like my head is full and swollen. At first I imagined "brain tumor" but after a few years I realised it should have surely killed me by now.
I've also gone the route of making an effort to be as healthy as I possibly can - eating right, taking supplements, exercising, getting enough sleep. That gives me some reassurance.
But at the end of the day I've realised that everyone has some sort of twinge, ache or pain almost every day. Normally one wouldn't even notice it. Someone with HA will exaggerate it and make it into an "illness".
Life isn't much fun skipping from one disease to another. I just wish I had the answers.